The present invention relates to processes for the distillation of liquid products applied for fractionation of hydrocarbon liquids and concerns directly to a method and a system for separation of liquid mixtures into their components.
Operational methods and systems for the vacuum distillation of liquids are known, which comprise a heat-mass exchange apparatus constituting a vacuum column with pipes for feed of a pre-heated stock product and for bleeding of extracted fractions, and a jet vacuum pump constituting a steam ejector connected with a separator. The steam ejector provides for evacuation of gases and vapors of volatile fractions from the top of the vacuum column. The separator is intended for separation of a liquid phase from the steam-liquid flow (see xe2x80x9cGuide for petroleum processorxe2x80x9d, book of G. A. Lastovkin, Leningrad, xe2x80x9cChemistryxe2x80x9d Publishing house, 1964, page 74).
The main imperfections of these methods and systems are large losses of desired product entrained with a motive (ejecting) medium of the vacuum-producing device, contamination of the motive steam with the desired product and consequent high energy consumption taking place during purification of the motive steam condensate formed in the separator.
The closest analogue regarding both a method and a device, which has been chosen as the starting point for the present invention, is the invention (variants) and system for realizing the same introduced in the patent RU No 2050168, M. cl. B 01 D Mar. 10, 1992. This invention teaches a process for the vacuum distillation of a liquid (oil stock mainly) and a plant realizing this process.
The starting point process consists of the feeding of a liquid into an evacuated reservoir, evacuation of gases and vapours from the reservoir by a vacuum-producing device and further condensation of the evacuated gases and vapors.
An imperfection of this process is a poor quality base product after separation which requires after-purification of the base product and which results in additional expenses.
The system proposed in said RU patent for realization of this process comprises an evacuated reservoir with a pipeline for bleeding gases and vapours, and a vacuum-producing device constituting a circulation system composed of a liquid-gas jet ejector, a separator and a pump.
This system possesses the same imperfection: after-purification of the produced distillate is required, which results in extra expenses.
The technical problems to be solved by the present invention relate to improving fractionation quality of a hydrocarbon stock product during its distillation and increasing the environmental safety of the system.
The stated technical problems can be resolved using some features of polar and nonpolar liquids. It is known that all substances belong to one of the two big groups: polar substances and nonpolar ones. Molecules of polar substances contain non-uniformly arranged polar covalent bonds and have a non-uniform distribution of exterior electrons. Molecules of nonpolar substances contain nonpolar covalent bonds with equal attraction for shared electrons and a resulting balanced distribution of charge. One of the features of such substances is that usually a polar liquid substance can not form a homogeneous mixture with a nonpolar liquid substance. The two substances can form only an emulsion, i.e. a colloidal suspension of one liquid in another liquid. According to modern conceptions, two types of emulsions are discerned subject to the nature of a dispersion phase: emulsions of the first sort (or direct emulsions, i.e. emulsions of a nonpolar liquid in a polar liquid, for example oil/water) and emulsions of the second sort (i.e. emulsions of a polar liquid in a nonpolar liquid). Emulsions of both sorts are kinetically and aggregately unstable systems because they constitute coarse dispersions. A coalescence resulting in breaking of emulsions into uninterrupted liquid layers within a short period of time is one of the properties of said dispersions. In contrast, two polar or two nonpolar liquids can form a stable homogeneous mixture or a solution.
With regard to the method as the subject-matter of the invention the above mentioned objectives can be attained using a method for vacuum distillation of a liquid product, which includes the steps of:
feeding a nonpolar liquid product into an evacuated reservoir;
feeding a polar liquid as a motive liquid of a vacuum-producing liquid-gas jet apparatus;
evacuating a nonpolar gas-vapor medium from the reservoir by the vacuum-producing liquid-gas jet apparatus;
condensing the evacuated nonpolar gas-vapor medium by the motive liquid flowing from a nozzle of the liquid-gas jet apparatus;
forming a mixture in the liquid-gas jet apparatus of a gaseous phase and a liquid emulsion having the polar liquid and a nonpolar condensate having a condensable component of the evacuated nonpolar gas-vapor medium;
disengaging the mixture into the gaseous phase and the liquid emulsion and simultaneously separating the liquid emulsion into at least two continuous layers, one layer having the polar liquid and another layer having the nonpolar condensate;
discharging the gaseous phase after said step of disengaging the mixture into the gaseous phase and the liquid emulsion;
withdrawing the nonpolar condensate after the step of separating the liquid emulsion into at least two continuous layers;
recycling the polar liquid after the step of separating the liquid emulsion into at least two continuous layers by pumping the polar liquid back into the nozzle of the vacuum-producing liquid-gas jet apparatus as the motive liquid.
Practically the same method with only one distinction can be applied for the vacuum distillation of a polar liquid product. This distinction is that a nonpolar liquid must be used as the motive liquid of the vacuum-producing liquid-gas jet apparatus in the case where a polar liquid is to be distilled and consequently where an evacuated gas-vapor medium consists of polar components only.
There is another variant of the introduced method which can provide a solution to the stated technical problems in the case where an evacuated gas-vapor medium consists of nonpolar components and at least one polar component. In this case the method includes the steps of:
feeding a liquid product into an evacuated reservoir;
feeding a polar liquid as a motive liquid into a vacuum-producing liquid-gas jet apparatus;
evacuating a gas-vapor medium having a nonpolar component and at least one polar component from the reservoir by the vacuum-producing liquid-gas jet apparatus;
condensing the evacuated gas-vapor medium by the motive liquid flowing from a nozzle of the liquid-gas jet apparatus;
forming a mixture in the liquid-gas jet apparatus of a gaseous phase and a liquid emulsion having the polar liquid, a polar condensate from the at least one polar component of the evacuated gas-vapor medium, and a nonpolar condensate from the nonpolar component of the evacuated gas-vapor medium;
disengaging the mixture into the gaseous phase and the liquid emulsion;
mixing the polar condensate with the polar liquid and consequently forming homogeneous polar liquid medium;
separating the liquid emulsion into at least two continuous layers, one layer including the homogeneous polar liquid medium and another layer including the nonpolar condensate;
discharging the gaseous phase after the step of disengaging the mixture into the gaseous phase and the liquid emulsion;
withdrawing the nonpolar condensate after the step of separating the liquid emulsion into at least two continuous layers;
withdrawing a surplus amount of the homogeneous polar liquid medium which is equal in amount to the polar condensate;
recycling the remainder of the homogenous polar liquid medium after the step of separating the liquid emulsion into at least two continuous layers by pumping the remainder of the homogenous polar liquid medium back into the nozzle of the vacuum-producing liquid-gas jet apparatus as the motive liquid.
If an evacuated gas-vapor medium consists of polar components and at least one nonpolar component, the method includes the steps of:
feeding a liquid product into an evacuated reservoir;
feeding a nonpolar liquid as a motive liquid of a vacuum-producing liquid-gas jet apparatus;
evacuating a gas-vapor medium having polar components and at least one nonpolar component from the reservoir by the vacuum-producing liquid-gas jet apparatus;
condensing the evacuated gas-vapor medium by the motive liquid flowing from a nozzle of the liquid-gas jet apparatus;
forming a mixture in the liquid-gas jet apparatus of a gaseous phase and a liquid emulsion having the nonpolar liquid, a nonpolar condensate from the at least one nonpolar component of the evacuated gas-vapor medium, and a polar condensate from the polar component of the evacuated gas-vapor medium in the liquid-gas jet apparatus;
disengaging the mixture into the gaseous phase and the liquid emulsion;
mixing the nonpolar condensate with the nonpolar liquid and consequently forming a homogeneous nonpolar liquid medium;
separating the liquid emulsion into at least two continuous layers, one layer including the homogenous nonpolar liquid medium and another layer including the polar condensate;
discharging the gaseous phase after the step of disengaging the mixture into the gaseous phase and the liquid emulsion;
withdrawing the polar condensate after the step of separating the liquid emulsion into the at least two continuous layers;
withdrawing a surplus amount of the homogenous nonpolar liquid medium which is equal in amount to the nonpolar condensate after the step of separating the liquid emulsion into the at least two continuous layers;
recycling the remainder of the homogenous nonpolar liquid medium after the step of separating the liquid emulsion into the at least two continuous layers by pumping the remainder of the homogenous nonpolar liquid medium back into the nozzle of the vacuum-producing liquid-gas jet apparatus as the motive liquid.
With regard to the apparatus as the subject-matter of the invention, a solution to the mentioned technical problems is provided by using a system for vacuum distillation of a liquid product which implements the introduced method and variants. The system has an evacuated reservoir with a pipeline for evacuation of a gas-vapor medium and a pipeline for discharging a distillation residue. Further, it includes a vacuum-producing device connected to the pipeline for evacuation of a gas-vapor medium and constituting a circulation system composed of a liquid-gas jet ejector, a separator and a pump. The separator is furnished with a pipeline for withdrawing a motive liquid, a pipeline for withdrawing a condensate of the evacuated gas-vapor medium and a pipeline for discharging a gaseous phase. One end of the pipeline for withdrawing a motive liquid is connected to a section of the separator where a layer of the motive liquid is accumulated after breaking of a liquid emulsion entering the separator into layers. Another end of this pipeline is connected to a suction port of the pump. The pipeline for withdrawing a condensate of the evacuated gas-vapor medium is connected to a section of the separator where a layer of the condensate of the gas-vapor medium is accumulated after breaking of the liquid emulsion entering the separator into layers.
In applications which require evacuation of gas-vapor mediums composed of nonpolar components and at least one polar component, a surplus amount of a polar liquid medium is generated during operation of the system due to condensation of the at least one polar component and subsequent mixing of the so formed polar condensate with the polar motive liquid in the separator. In applications which provide for evacuation of gas-vapor mediums composed of polar components and at least one nonpolar component; a surplus amount of a nonpolar liquid medium is generated during operation of the system due to condensation of the at least one nonpolar component and subsequent mixing of the so formed nonpolar condensate with the nonpolar motive liquid in the separator. Therefore in such applications the separator of the system must be furnished additionally with a pipeline for withdrawing the surplus amount of appropriate liquid medium which is equal in amount to the condensate which mixes with the related motive liquid.
Also, in the case where an evacuated medium includes both polar and nonpolar components, generally, it is preferable to use a polar motive liquid when the amount of a polar component (or components) of an evacuated medium is much smaller than the amount of a nonpolar component (or components) of the evacuated medium. And vice versa, it is better to use a nonpolar motive liquid when the amount of a nonpolar component of an evacuated medium is smaller than the amount of its polar component.
Generally, more than two liquid layers can be generated in the separator of the introduced system subject to particular composition of the liquid emulsion. Liquids accumulated in each of the layers can be removed separately. As a result, it is possible to avoid contamination of the liquid phases discharged from the separator and to use these phases as base products.
It turned out that the application of the introduced methods for distilling a liquid product by vacuum and related system can substantially improve effectiveness of the vacuum distillation and quality of the desired products, as well as eliminate such process stages as after-purification of the desired products. Consequently, additional expenses can be avoided.
Some other features of the invention will be clarified by the following examples of the realization of the invention.